Lymphocytes from patients with chronic inflammatory bowel disease are cytotoxic for allogenic colon epithelial cells. This effect exhibits both tissue and disease specificity and may be important to the pathogenesis of these disorders. An interaction between sensitized lymphocytes and bacterial antigens appears to be fundamental to this effect. The relationship of this in vitro cytotoxicity to the pathogenesis of chronic inflammatory bowel disease is at present conjectural, however. We, therefore, propose to study lymphocyte-bacterial antigen interaction in the production of an experimental colitis in guinea pigs manifesting cellular sensitivity to this antigen. The establishment of such an animal model would be unique in the study of chronic inflammatory bowel disease in that it utilizes the same antigen known to influence the effect of human lymphocytes on allogenic colon epithelial cells in vitro. Positive results would enhance the pathogenetic significance of the human data and facilitate further study of the cytotoxic effect.